1. Field of the Invention
The invention relates to storage units, and more particularly, to storage units capable of retaining data during sleep mode.
2. Brief Discussion of the Related Art
With advances in semiconductor process technology, system on chip (SOC) technology is widely used. Because most semiconductor circuits using system on ship technology are digital circuits, it is important to develop digital circuits with high performance and lower power consumption. Further, in digital circuits, register file (RF) is the most used circuit block, transferring and storing data at high speeds in addition to microprocessor and arithmetic logic unit (ALU).
FIG. 1A shows a conventional single-end storage unit. As shown, the storage unit 100 is controlled by three read control signals re1-re3 and a write control signal wr. The storage unit 100 can maintain latched data in the sleep mode. The storage unit 100, however, experiences current leakage under nanometer process. FIG. 1B shows another conventional single-end storage unit. As shown, the storage unit 100″ reduces current leakage in sleep mode by the transistor MS. Write and read operations of the storage units 100 and 100″ are similar to those of static random access memory (SRAM).
However, even in sleep mode, data stored in the storage units still may be lost over time, requiring rewrite of the lost data by the host system or an external storage unit when reverting to operating mode from sleep mode. However, the external storage unit not only increases chip area and cost but also dynamic power consumption during rewriting in addition to that caused by current leakage.